1. Field of the Invention
The present invention relates to a signal processing apparatus, a signal transmitting system, a signal processing method for executing the signal-processing for a Manchester-encoded digital signal.
2. Description of the Related Art
The Manchester-encoding is widely used as a modulating method for transmitting a digital signal at a high rate.
For example, when a digital signal is transmitted at a high rate, it is widely executed to separate, with a capacitive-coupling, DC levels of a transmitting unit and a receiving unit in a high rate transmitting line so as to absorb the influence of the DC levels between the transmitting unit and the receiving unit. When the DC levels are separated as described above, the Manchester code is adopted to maintain a DC balance between the transmitting unit and the receiving unit, in which the number of “H” (or, “1”) signals and the number of “L” (or, “0”) signals are equal to each other in a binary digital signal.
A method is known in which wide electrodes are capacitive-coupled by causing the electrodes sandwiching insulation material to face each other without contacting to each other, and a signal is transmitted by wireless, and in such a case, the Manchester code is used so that the signal can be also transmitted where a transmission rate is increased and a coupling capacity is small.
When the Manchester code is used as described above, as illustrated in FIG. 7, an original signal is encoded to the below-illustrated Manchester code by a Manchester-encoding circuit (or, a modulating circuit for the Manchester-encoding).
In the Manchester-encoding, the original signal is converted to a digital signal by assigning two bits of “10” to any one of the original signals “0 and “1”, and two bits of “01” to the other original signal. Meanwhile, a term length of each of “10” and “01” is equal to a term of one bit of the original signal. Such a case is illustrated in FIG. 7 that “10” is assigned to the original signal “0”, and “01” is assigned to the original signal “1”.
FIG. 7 illustrates, below the Manchester code, a relation between the first bit and the second bit corresponding to the Manchester-encoding.
When such a Manchester code is decoded in the receiving side, as described above, since the Manchester code has been encoded to a signal whose term of one piece corresponds to a half term of the original signal, to a signal whose frequency is double of that of the original signal, when the decoding is processed at the frequency of the encoded signal, the power consumption increases.
For example, Japanese Patent Application Laid-Open Publication No. 8-191269 discloses an apparatus as a first prior example, in which the optical communication is executed by using the Manchester encoding and decoding.
In the apparatus, a transmitter Manchester-encodes data by using a clock, and transmits the encoded data as an optical signal. A receiver side generates a difference signal which is a difference between the received optical signal and a signal power a half bit before the received optical signal, and decodes (signal-reproduces) the difference signal by using a clock.
The clock is a clock whose frequency is the same as that of the clock of the transmitting side. One cycle of the clock corresponds to two bits of the Manchester-encoded signal, and a signal processing unit corresponds to a term of one bit of the Manchester-encoded signal.
Meanwhile, Japanese Patent Application Laid-Open Publication No. 2006-287052 discloses a capacitive-coupling apparatus as a second prior example, in which a signal can be transmitted even in such a structure that one side is rotated.